Generally, areas such as mountains, valleys and underground receive a weak transmission or are isolated completely from any radio waves due to the geographical situation. Thus, many base stations must be constructed to provide communication services in these shaded areas, requiring costly equipments and management. As the demand for communication services rises, the cost also increases, thereby creating a problem.
As one solution to this problems, a fiberoptic repeating system has been proposed and is currently being used commercially. However, a considerable amount of signal damping results in the optical cables of such a fiberoptic repeating system. Therefore, to compensate the signal damping, a gain control unit has also been proposed for the fiberoptic repeating system.
A fiberoptic repeating system in the related art generally includes a base station 1, a master repeater 2, and one of a plurality of a slave repeaters 3, as shown in FIG. 1. The slave repeater 3 receives and/or transmits RF signals within a remote region, and the master repeater 2 relays data between the base station 2 and the slave repeater 3.
More specifically, the master repeater 2 includes a driver amplifier 20 which amplifies an RF signal transmitted from the base station 1; an optic/RF converter 23 which converts from an amplified RF signal received through the driver amplifier 20 into an optic signal for transmission through an optical cable 4 or from an optic signal transmitted through the optical cable 4 into an RF signal; a master repeater controller 21 which monitors an operational state of the elements of the master repeater 2, controls the operation of the master repeater 2 or the slave repeater 3 according to a control signal of the base station 1, detects a level of RF signal amplified through the driver amplifier 20 and outputs the detected level as a digital reference value; and a MODEM 22 which modulates the output of the master repeater controller 21 and transmits the output to the slave repeater 3 side through the optic/RF converter 23.
The slave repeater 3 includes an optic/RF converter 31 which converts an optic signal transmitted through the optical cable 4 into an RF signal or converts an RF signal received through a receiving antenna into an optic signal for transmission through the optical cable 4; a driver amplifier 30 and a high-power amplifier 34 which amplifies an output of the optic/RF converter 31; a low noise amplifier 35 which amplifies the RF signal received through the receiving antenna and transmits the amplified RF signal to the optic/RF converter 31; a MODEM 32 which demodulates the digital reference signal received through the optic/RF converter 31; and a slave repeater controller 33 which detects a level of the RF signal received through the optic/RF converter 31, compares the detected level with a digital reference value transmitted through the MODEM 32, and adjusts a gain level of the driver amplifier 30 to compensate the difference.
The signal transmission and reception operations in the fiberoptic system of FIG. 1 is as follows.
An RF signal is received through a receiving antenna of the slave repeater 3 and is amplified by a constant level through the low noise amplifier 35. The amplified RF signal is then transmitted to the base station 1 via the optic/RF converters 31 and 23. Thereafter, the base station 1 transmits a corresponding RF signal to an appropriate terminal of a receiving party via the master repeater 2 and the slave repeater 3.
Particularly, the RF signal transmitted by the base station 1 is amplified by a constant level through the driver amplifier 20, and is converted into an optic signal through the optic/RF converter 23. Also, the master repeater controller 21 periodically detects a level of the RF signal output from the driver amplifier 20, converts the detected level into a digital MODEM RF signal level, modulates the digital MODEM RF signal level through the MODEM 22, and transmits the modulated digital MODEM RF signal level through the optic/RF converter 23.
The optic signal transmitted by the optic/RF converter 23 is demodulated into a digital MODEM RF signal through the optic/RF converter 31 and the MODEM 32 of the slave repeater 3, and is input to the slave repeater controller 33. The slave repeater controller 33 stores the level of the digital MODEM RF signal as a reference level. Also, the optic signal transmitted by the optic/RF converter 23 is converted into a RF signal through the optic/RF converter 31 and input to the driver amplifier 30. Thus, the slave repeater controller 33 converts the RF signal input to the driver amplifier 30 into a digital signal, compares the level of the digital signal with the reference level, and controls a gain level of the driver amplifier 30 to compensate a damping of the RF signal level by the differential value. Accordingly, the RF signal with a compensated signal level is amplified into a radio-transmittable level by the high power amplifier 34, and is transmitted to a corresponding terminal through the transmission antenna.
Furthermore, the master repeater controller 21 of the master repeater 2 and the slave repeater controller 33 of the slave repeater 3 respectively monitor the operational states of elements 20˜23 and 31˜35. Accordingly, when a specific control signal, e.g. a gain control signal of the slave repeater 3, is transmitted from the base station 1 to the master repeater 2, the master repeater controller 21 modulates the corresponding gain control signal through the MODEM 22 and transmits the modulated gain control signal to the slave repeater 3. The slave repeater controller 33 demodulates the gain control signal through the MODEM 32, reads the content of the gain control signal and controls a gain of the driver amplifier 30.
In the fiberoptic repeating system as described above, the RF signal levels are periodically detected and become reference signals for calculation of the damping rates of the RF signal levels to compensate the gain damping. Thus, the intervals for the periodic detection of the reference levels must be short in order to deal with the frequent change of the RF signal levels. As a result, the control operations of a base station cannot always be executed for each determination of the reference level within the given interval.